Radio pulse duplexing system



June 27, 1950 R. M. PAGE 2,512,673

RADIO PULSE DUPLEXING SYSTEM Filed June 8, 1948 ANTENNA kmy 15 RECEIVER R.F. PULSE TRANSMITTER 5 III-172E gg 2000 2000 2000 200a 2000 '8 RECEIVER ANTENNA INVENTOR. ROBERT M PAGE ATTORNEY Patented June 27, 1950 U N I TED S TATE S F Fl-CE RADIO PULSE DUPLEXING- SYSTEM Robert M.I,age, Washington,-D. 0.

Application June 8, 1948; 1Serial-No. 8 1,'7'79 (Granted under the act of March ;3, 1883, as

amended April 30, 1928; 370 0. G.757)

' 2 Claims.

This invention relates ,torimprovements in duplex transmission systems and articularly to high'frequency radio systems utilizing a single transmission line for thetransmission and reception of pulse signals.

.The present invention is particularly concerned with radio pulse systems wherein a single transmission line is employed to transmit recurrent high powered pulses to a first load circuit and alternately recurring low powered pulses to a second load circuit which usually comprises delicate, sensitive, receiving equipment.

The practicability of such systemsdependson -the--effectiveness of theapparatus'used for decoupling the receiving equipmentffromthe antenna during the high powered transmission in- "tervals, namely, the completeness of receiver deprovide an improved andmore. efiective receiver ,protective device for duplex radio pulse systems.

-Itis another object of this invention to provide .an improved and more efiicient receiver .load protectivedevice for duplex radio pulse systems offer- .inggreatly improvedreceiver protection char- --;acteristics.

L Iti;is;;still another object of this invention to providean improved and more efficient receiver :.-protective device. for duplex radio pulse systems aofiering: greatly improved energy transfer characteristics betweenqthe transmission circuit and the'receiver-load circuitduring the period;o1

transmitterinoperativeness.

In certain types of radiov pulse. systems, the

'- transmitting apparatus used therewith exhibits an impedance match to the output transmission line during periods of transmitter inoperativeness andan impedance mismatch during periods of transmitter inoperativeness. In such systems, a critical length of transmission line is used to couplethe .transmitter to the mainline. This 1?. line section cooperates with the changing im- ..pedance characteristics of. the transmitter tojde- .ucql ple. thetransmitter from the. main transmis- 2 sion line duringthe; period of inoperativeness. ;In other systems, however, the transmitter impedv:ance dcesnot change materially and some means for automatically decoupling the transmitter .0, themain li us provide 1 11 a c ordingly another object of this invention to provide such a device.

:It is another object of this invention I to prc- --,vide .a transmitter decoupling; device forduplex p ls rad system o erin r r at xim rqved:d

' co ;.chara t rist c It isstill another object ofwthis'invention to pp vid an. improv d an .er at vmo e emei transmit-receive sw h for .ra io. pulse uD ,;syst ems automatically; operative during periods 0f !.high powdered transmission to decouple the :receiver from .the main line and further auto- .matically operative during periods Of receptionto decouple. theiztransmitter from the main line.

Other and more specific objects andattainments of the present invention will becomeapparent upon acareful consideration of the following detailed description when taken together with the accompanying drawings, which:

Fig. 1 is a'simplified cross sectional view of a rece ver load-protective deviceconstructed in accordance with the-teachings of the invention,

Fig. ;2 is a simplifiedcross sectional view of, a transmitter-receiver decoupling device also made in accordance with the teachings of the present invention.

In Fig. 1 to which reference. is now had, there .is disclosed my novel receiver protective device Mas applied to a duplex radio pulse system. As

indicated in the drawings, an antenna lil or any other suitable loadis connected through the main transmission line II to radio frequency pulse transmitter l2 and alsothrough Tejunction l3 andload decoupler It to receiver l5.

.In. this. particular, application, the radio fre- ,quency pulse transmitter i2 is preferabl-y -of -the type.- which changes .impedances between opera- ;;-tion; and quiescence. ,Accordingly, if transmitter 12 ,isof the type which exhibitsa high impedance durin p r ods or -qui cence h nt tlenet 0f the transmission line i Lbetweenthe transmitter and the junction l tqshould .be made :equal :toan even numberof quarter .wave lengths .to provide maximum decoupling of -the-transmitter. Conversely,-if transmitter 12 is of the type which exhibits a low-output impedance during periods of u escence then the length of 1 the line I l between pulse transmitter l 2 and junction "I 3 should. equal an odd number of quarter wave lengths for optimum decoupling of the transmitter. In either event, the length of the transmission line II connecting junction point I3 and transmitter I2 is generally chosen so as to provide maximum decoupling of the transmitter from the antenna during the periods of transmitter quiescence.

Again as indicated in the drawing the receiver protective device I4 as herein illustrated comprises a concentric line which is equal to an odd number of wave lengths long, which, in this particular illustration is chosen to be equal to three half wave lengths long. One end of the protective device is terminated in the main line I I at junction I3 and the outer end is terminated in a short-circuiting tuning plunger l 8. Plunger I6 is a generally annular cup shaped member of conventional design adapted to provide a movable short circuit between the inner and outer conductors MA and MB of device It. To provide impedance matching at the output tap ISA, plunger I6 is made movable. Output line I8 is preferably a conventional coaxial conductor the inner and outer members of which are connected respectively to the inner and outer conductors of the device I4 at a point which suitably matches the input impedance to line I8. A stub line sec tion I! is connected to the device I4 preferably at the output tap IBA and is provided with a movable plunger I9 similar to plunger I6 operable to tune out the reactance of device I I at the point of the output connection to line I8.

Inserted across the inner and outer conductors HA and MB of device I4, at a point an odd quarter wave length removed from junction I3 is a suitable non-linear impedance element 20 which in this instance is a spark gap enclosed within a glass envelope 20C. Impedance element 20 is provided with two electrodes 20A and 20B which connect respectively to the inner and outer conductors MA and MB of device I4.

The purpose of the non-linear impedance element is to provide an element in the circuit which exhibits a high impedance when subjected to low power impulses, such as echo signals, and to exhibit low impedance to high poweredimpulses such as those emitted directly from the transmitter I2.

More particularly, during periods of transmitter quiescence, the spark gap 20 is effectively deionized and appearsas an open circuit across the inner and outer conductors MA and I 43 of device I4. In this condition the receiver I is matched to the line I I and also to the antenna Ii). During periods of transmitter operation however, gap 20 becomes ionized by the transmitted power and thus becomes a low impedance across the decoupler line I I. Now then, since gap 20 is disposed across the decoupler line section Idat a point which is an odd number of quarter wave lengths removed from the junction I3 the impedance of device 20 will consequently be inverted at the junction I3. Accordingly, the low impedance of gap 20 during its ionized condition will be reflected as a high impedance at junction I 3. Thus the impedance looking into the decoupler line section I 4 at junction l3 will be greatly mismatched from the line impedance of the main Systems operating in the above described manner and having the same general characteristics are now well known in the art and it can be generally said that they offer adequate protection to.

the receiver under low and medium low trans 4 mitted power conditions. The amount of receiver protection of course depends upon the mismatch in impedances which can be obtained at the junction I3 and this in turn is directly proportional to the square of the characteristic impedance of the line section I4 and inversely proportional to the impedance of the gap in an ionized condition. Accordingly, the impedance of the gap and the characteristic impedance of the line section I4 jointly operate to limit the amount of protection which can be provided for the receiver.

If the ionized impedance of the gap 20 could be reduced to zero then complete protection of the receiver would result with the above operation. Such is not the case, however, since under the most favorable conditions the ionized impedance of the gap 28 is often as large as 40 ohms. A gap displaying a minimum impedance of this magnitude will not afiord complete receiver protection when installed in the and 200 ohm lines that are now in present day use. For example, a gap displaying this magnitude of impedance when installed in an 80 ohm line would produce a surge impedance at junction I3 of only ohms and when installed in a 200 ohm line would produce a surge impedance of only 1000 ohms.

With the present invention, however, a gap having an ionized impedance similar to that described above can be employed to provide almost complete receiver protection. Specifically, in the preferred embodiment herein shown, which it must be understood is only exemplary, I can obtain a surge impedance at junction I3 which exceeds 6000 ohms.

Briefly and in accordance with the fundamental concepts of the invention, the Protective line section I4 is constructed to provide a transmission path offering alterant high and low impedance points therein. The gap 20 is then disposed at a high impedance point while the receiver or load output tap is taken at an impedance matching point. In this manner the relatively low ionized impedance of the gap is transformed into an extra high impedance at the junction I 3.

In particular I accomplished the foregoing objective by employing a series of impedance transformer sections, or odd quarter wave length line sections of alternately high and low characteristic impedance. As shown in the drawings these line sections are formed by using a common and continuous outer conductor MB of a fixed diameter and an inner conductor having alternately constricted and enlarged diametrical dimensions. As further indicated in the drawings, which is taken to illustrate a typical condition where the main transmission line I I and the receiver transmission line I8 are both of the 80 ohms, the inner conductor of thereceiver protection line I I adjacentjunction I3 is constricted in diameter to provide a 200 ohm line section of one quarter wave length. Immediately following thisline section is an enlarged inner conductor section forming an 80 ohm line section also of a. quarter wave length long. This last section is then followed by another constricted inner conductor section forming another 200 ohm line section. The gap 20 is located at the end of this last section. Then from the gap 20 proceeding to the receiver connection I3a, a 200 ohm line section and an 80 ohm line section follow.

These line sections are so organized that the receiver I5 is matched to the main line II during the intervals that gap 20 isfdeionized. When gap setgi lt'itn'tt a1 airspace-seen,

lident .lthat with a given gap impedance -the 'grnismatch looking into the protective device at 3 can be raised by a f'aQtdI"Qf ;6 A1 times over that obtainableby the use of a straight200line section connecting the gap to the main line II. This arrangementv affordealmost complete rece iver.protection and can be obtained by using. standard components. Again, it is here to be expresslybnderstood that the embo'diment illustrated in'Fig. 1 is only exemplary and that in actual practice theline =.-s c ion. [Am r akgwqther iprmssu as n ord ana y' par leLwi ie lin L kewi the h a -H.

istic impedance, of thesuccessive quarter wave length line section m'ay'assui'ne' values distinct to that shownin the drawings...

.:,i...Apparatus, whichis exemplary of the present tel-eta 1 same b l nineas s ent. fin

p a consumption of transmitted energy 'therjepyf ai- 'fo'rding better coupling eniciency between-the se off so, locating gap I; isjt lr l ii l {its transmitter and the antenna'diiringperiods'of transmission. v V

,In operation, emission of a pulse from transinitterglzlionizes'the bothgapst and 20. xemzation "oij gap '20 operates to insert a low -ini- 'ioI.

pedance across device 5|! fat a point t ree uarters'o'f a wave length removed irom thejunc- 'jtijon l3. 'Thislow" impedance, as hereinabove described isjtran'sformed into a high impedance at junction [3 and thus operates to decouple the receiver from the transmitter. I I

"Ionization of gap 5| simply 'completes'the-cir- I cuit enablingenergy to'be propagated'fromthe transmitter 12 to the "antenna Ill. It willbe "noted that in the ionized condition or the gaps 5| and junction I3 is terminated in the-impedance of line H since gap 2|! reflectsan effectiveopen circuit at junction l3 at'this instant.

invention and which is adapted to perform the composite function of transmitter and receiver decoupling is illustrated in Fig. 2, to which reference is now had. In this embodiment the transmitter |2 and receiver l5 are each coupled to the antenna ID through separate ections of the transmit-receive device 50.

In general device 5|] utilizes the same principles of operation and construction as employed in the receiver protective device M of Fig. 1. In particular, that portion of device 50 coupling the receiver |5 to the antenna ID is identical to that illustrated in Fig. 1. For instance, the same arrangement of impedance transformation means are used to build the surge impendance up to a suitable level for installation of the gap 20. The latter element is again disposed in the transmission path at a point three quarter wave lengths removed from the antenna junction point l3.

Accordingly, since the receiver decoupler portion of device 50 is structurally and functionally identical with the corresponding element l4 shown in Fig. 1 no further explanation thereof is deemed necessary.

Referring now to the transmitter decoupling portion of device 50 it will be seen that thi element is somewhat similar to the receiver decoupler. In particular, the transmitter decoupler comprises a serie of tandemly connected impedance transformer sections arranged to provide alterant high and low surge impedance points along the line. A second non-linear element indicated at 5| is inserted in series with the inner conductor of the line section at a point of high impedance.

In the embodiment herein exemplified the transmitter decoupler comprises in particular, a forty ohm quarter wave section at junction I3 followed by a 200 ohm quarter wave section, which is terminated in the series spark gap 5|. Following the gap 5| is another 200 ohm quarter wave section and then another ohm quarter wave section, and finally an 80 ohm one half wave section terminating in the shorting circuiting plunger l6 added for the same purpose as plunger I6. A second stub line H and associated tuning plunger l9 are added for the same purpose as their counterparts l1 and I9.

The transmitter I2 is tapped in to device by line H at a point providing impedance matching.

Gap 5| like gap 20 is located at a high im- In this conditionassuming line H to"'be"80'ohms for" example and the impedance "of antenna" I0 is matched to line ||,'then the'surge" impedance appearing at point D looking toward junction I3 becomes 20 ohms. The surge impedance at gap 5| in this condition is 200 ohms. Hence gap 5| is at a high impedance point (low current) in theline and the low ionized impedance, 40 ohms, of gap 5| is negligible by comparison. Thus the power loss in gap 5| is also negligible and a very eflicient coupling between the transmitter and the antenna results. The 200, 40 and ohm sections interposed between the gap 5| and the end of the line act to lower the high surge impedance appearing at the gap to a level suitable to match the output impedance of the transmitter.

In operation, during reception both gaps 20 and 5| are deionized with the result that the antenna is coupled to the receiver l5 in the manner previously described. Gap 5| in this condition appears as an open circuit and since it is one half wave length removed from junction l3 the same will reflect an open circuit at this joint.

It will be apparent from the foregoing that the present invention provides a greatly improved and more efiicient transmitter receiver decoupler than provided by the prior art. It will also be recognized that by the use of impedance transformation sections to build up the impedance to a high level for insertion of the spark gaps, or other non-linear elements, it is possible to minimize the power loss in these elements thereby increasing not only the operating efficiency of the apparatus but also increasing the life of the gaps themselves.

Accordingly, although I have shown only one specialized embodiment of the present invention it is to be expressly understood that I am fully aware of the many modifications possible thereof. For example, the non-linear elements 20 and 5| need not be of the spark-gap type since ordinary thermionic diodes also may be used.

Likewise, it is also within the spirit of this invention to construct the devices l4 and 50 from a line section having a uniform inner diameter and alternately enlarged and constricted outer diameters. Similarly, alternate types of transmission line sections may be utilized. For example, the invention may readily be applied to a parallel line if desired. Accordingly, the scope of this invention is not to be limited except insofar as is defined in the appended claimS' -7 The invention described hereinmay be manufactured and used by'or for the Government of thefUnited'States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is: 1. In combination, a source of intermittent radio frequency power, firstand second load circuits, a transmission circuit connecting said source of power to the first load circuit comprising; a series of impedance transformation means tandemly connected to provide a transmission path having alternate high and low impedance points therein, a non-linear impedance element incorporated in said transmission path at a high impedance point, a similar transmission path connecting the source of power to the second load, and a second non-linear element incorporated in the last named transmission path at a high impedance point therein.

2. In combination, a source of intermittent radio frequency power, first and second load circuits, a transmission circuit connecting said source of power to the first load circuit comprising, a series of impedance transformation Vmeans tandemly connected to provide a trans- REFERENCES CITED The following references are of record in the file of this patent:

, UNITED STATES PATENTS Number Name Date 1,035,958 Girardeau Aug. 20, 1912 2,438,367 Keister Mar. 23, 1948 OTHER REFERENCES Principles of Radar, MIT Radar'School Staff, second edition, published 1946 by McGraw-Hill Cc. 

